This is a competing continuation application whose overall goal is to ensure that resin-based materials which are placed onto teeth as part of dental care can continue to be used safely. Resin based materials which polymerize in the mouth are now used by dentists in many ways to help prevent tooth decay and for tooth repair and replacement. Bonding technologies, which are all based on this class of materials, are used for fissure sealing to help prevent decay, for bonding orthodontic brackets to teeth, and as part of many different types of tooth repair to improve appearance and function. It is very likely that new and modified materials of the same general type will continue to be developed and that the use of this type of material in dentistry will continue to increase in the coming years. The materials are very helpful to patients and have remarkably few negative side effects. However, severe allergic dermatitis in some dentists and other dental workers is linked to the use of the materials, and the incidence of such allergy appears to be increasing. Fortunately, allergic responses are less common in patients, but we do not know why this is so or whether it will continue to be so. Some patients experience pain in the dental pulp after resins are used in deep fillings, for reasons that may be related to direct chemical damage caused by released chemicals, by allergy to them, or to both. It has previously been shown in laboratory studies that two chemicals are released from these materials during the first days after they are placed on teeth. The first aim will be to confirm this release in experimental animals (guinea pigs), and study what happens to the chemicals in the body (their uptake, distribution, time of storage, breakdown and excretion). The second aim will be to study mechanisms of allergic responses to these chemicals at the cellular and molecular level using guinea pigs and mice. The third aim will be to determine whether there are differences between the risk of allergy with skin contact (as can occur in dental workers) relative to contact with the inside of the mouth and through tooth structure to the tooth pulp (as can occur in patients) in the same animals. The fourth aim will be to study allergic responses at the cellular and molecular level using blood and other tissues donated by volunteer dentists and other dental workers, to ensure that the experimental studies of the phenomenon using animal models and animal tissues in culture are valid. The studies described will help to prevent and treat adverse effects of this class of dental materials.